Minimum requirements for H1B travel with VISA from previous employer and valid job offer from another

Hello Everyone

I have H1B VISA stamped from my old employer and now trying to get hold of another to initiate the transfer. Must i get the transfer completed to (with approval notice) to become eligible to travel even on old visa? Can i travel with old visa while the transfer is in progress with just receipt notice and LCA? In other words, what is the minimum requirement of documents.

Many Thanks in advance